In recent years, a wireless LAN (Local Area Network) system, which is typified by IEEE (Institute of Electrical and Electronics Engineers) 802.11, has come into wide use instead of a wired network owing to advantages of a high degree of freedom of equipment and the like. For example, IEEE 802.11a/g has come into wide use and IEEE 802.11n is expected to become widely available in the future.
Currently, IEEE 802.11ac is supposed to be employed as a next-generation wireless LAN standard. The IEEE 802.11ac is expected to employ SDMA (Space Division Multiple Access) in which wireless resources on a spatial axis are shared among a plurality of users. SDMA enables simultaneous one-to-many communications using the same frequency, which makes it possible to seek a significant improvement of the transmission rate.
A fair number of wireless LAN systems avoid interference between wireless communication devices by access control based on carrier sense, such as CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).
For example, a wireless communication device performing data transmission transmits an RTS (Request To Send) packet and initiates transmission of a data packet upon receipt of a CTS (Clear To Send) packet from a wireless communication device of a transmission destination. Further, a wireless communication device having received at least one of RTS and CTS packets which are not destined for its own station sets NAV (Network Allocation Vector) based on duration information contained in the received packet to avoid interference. The interference avoidance based on the duration information is described in, for example, the following patent literature 1.